Abstract:Two successive long lived mesoscale convective systems (MCS A1, MCS A2) struck Pearl River Estuary of South China during 8-9 May 2014, and induced extreme precipitation over the region. From noon of 8 May MCS A1 sustained over than 11 h on land of South China, with slowly moving towards southeast from east of Guangxi to Pearl River Estuary in Guangdong. The successive MCS A2 sustained more than 9 h, inducing rainfall of more than 400 mm along the coast of the Pearl River Estuary from early morning to noon of 9 May. Weak cold surface layer sustained in the south of South China with weak surface temperature gradience on the morning of 8 May before the convection burst. The initialization of convection was connected with strengthening of surface south 〖JP2〗wind and topographic lifting near noon of 8 May. MCS A1 evolved from〖JP〗 training line/adjoining stratiform (TL/AS) to mesoscale vortex in convective organization under weak baroclinic environment. With propagation of surface cool pool due to MCS A1’s precipitation in the early night of 8 May, surface temperature boundary and wind convergence zone was pushed to the southwest coast of Guangdong. In the late night of 8 May MCS A1 moved out of land, then MCS A2 was developing adjointly to the remnant cool pool boundary induced by MCS A1 with low level southwest wind enhancing in the early morning of 9 May. MCS A2 was composed by multiple parallel meso β scale line type convective systems, the extreme rainfall was related with quasi stationary cool pool boundary, train moving cells in meso β scale line type convective systems with high precipitation efficiency. From late night of 8 May to morning of 9 May, the balance between cool pool outflow and low level vertical shear could sustain upright convective cells of MCS A2. In conclusion, with carefully researching on convective feedback to boundary and surface layer, the forecast skills could be improved for heavy rainfall events in weak synoptic forcing environment during the pre rainy season in South China.